1. Field of the Invention
The present invention relates to negative electrodes for rechargeable lithium batteries and rechargeable lithium batteries including the same.
2. Description of the Related Art
Lithium rechargeable batteries have recently drawn attention as power sources for small portable electronic devices. These batteries use organic electrolyte solutions that have discharge voltages twice as high as conventional batteries that use alkali aqueous solutions. Accordingly, lithium rechargeable batteries have high energy densities.
Lithium-transition element composite oxides capable of intercalating lithium, such as LiCoO2, LiMn2O4, LiNiO2, LiNi1−xCoxO2 (0<x<1), and so on, have been researched for use as positive active materials for lithium rechargeable batteries.
Carbon-based materials, such as artificial graphite, natural graphite, and hard carbon, all of which can all intercalate and deintercalate lithium ions, have been used as negative active materials. The use of graphite tends to increase discharge voltage and energy densities because graphite has a low discharge potential of −0.2V compared to lithium. Batteries using graphite as the negative active material have high average discharge potential of 3.6V and excellent energy densities. Furthermore, graphite is the most comprehensively used among the aforementioned carbon-based materials because graphite imparts better cycle-life due to its outstanding reversibility. However, when used as negative active materials, graphite active materials have low densities and consequently low capacity in terms of energy density per unit volume. Further, because graphite is likely to react with the organic electrolyte at high discharge voltages, there are some dangers such as explosion or combustion when a battery is misused, overcharged, or the like.
To address these problems, research in metal oxide negative electrodes including tin oxide, or lithium vanadium oxide, has recently been performed. For example, amorphous tin oxide, which has high capacity per weight (i.e. 800 mAh/g), has been suggested as an alternative. However, amorphous tin oxide has a high initial irreversible capacity up to 50%. Furthermore, tin oxide has a tendency to reduce to tin metal during the charge or discharge cycle, thereby rendering it disadvantageous for use in batteries.
In another metal oxide negative electrode, LiaMgbVOc (0.05≦a≦3, 0.12≦b≦2, and 2≦2c-a-2b≦5) has been used as a negative active material. However, such metal oxide negative electrode does not impart sufficient battery performance and therefore further research into metal oxide negative materials has been conducted.